1. Field of the Invention
The present invention relates to a record player of the direct drive system, and more particularly to a record player in which the torque of a motor is cancelled in order to eliminate rotational vibrations.
2. Description of the Prior Art
A prior art record player of the direct drive system is constructed as shown in FIGS. 1 and 2.
In the FIGS., numeral 1 designates a cabinet, on which a turntable 2 is turnably arranged. A motor 3 drives the turntable 2 so as to rotate at a predetermined speed. A tone arm 4 holds a cartridge including a stylus tip which traces the sound groove of a record or disk, not shown, placed on the turntable 2 and which converts it into an electric signal. The cabinet 1 is situated on a fixed member or place 6 such as a floor through insulators 5 which cut off vibrations.
In such a record player, a torque which is developed by driving the turntable 2 by means of the motor 3 is in the direction of arrow A indicated in FIG. 1, that is, in the CW (clockwise) direction. As a counteraction to this torque, a torque in the direction of arrow B indicated in FIG. 1 or in the CCW (counterclockwise) direction acts on the cabinet 1. In this regard, if the turntable 2 rotates at the constant speed and the torque developed by the motor 3 is constant with time, the counteractive torque on the cabinet 1 will also become constant with time. In general, however, the torque TQ.sub.a acting on the turntable 2, in other words, acting on the rotor of the motor 3, vibrates as a function of the time T as shown in FIG. 3. Accordingly, the torque TQ.sub.b acting on the cabinet 1, in other words, acting on the stator of the motor 3, fluctuates vibrantly as a function of time T in a phase opposite to that of the torque TQ.sub.a.
If the cabinet 1 has a great mass and is situated directly on the fixed member 6 so that both are rigidly coupled, then vibrations due to the torque TQ.sub.b will be very small. In such construction, however, vibrations from the side of the fixed member 6 or the so-called floor vibrations ascribable to the walking of the operator, etc. are directly transmitted to the tone arm 4 and give rise to the jump of the stylus, etc. Accordingly, the cabinet 1 needs to be situated on the fixed member 6 through the insulators 5. In the record player of FIGS. 1 and 2 provided with the insulators 5, the cabinet 1 undergoes rotational vibrations in relation to the torque acting on the cabinet 1 and the viscoelasticity of the insulators 5. The rotational vibrations vibrate the cabinet 1 and simultaneously vibrate the tone arm 4, resulting in the disadvantages that the reproduced signal of the disk is affected very adversely, especially a cross modulation or intermodulation distortion being caused, and that the signal-to-noise ratio is degraded.